1. Field of the Invention
The present invention relates to a conductive belt and more particularly to a conductive belt that is used suitably as a seamless intermediate transfer belt in image-forming apparatuses such as a copying machine, a printer, a facsimile, and the like.
2. Description of the Related Art
To impart an electrical conductivity to the transfer belt for use in the copying machine, the printer, and the like, the following two methods are conventionally used: In one of them, an electroconductive rubber containing a conductive filler is used for the transfer belt. In the other of them, an ionic-conductive rubber such as urethane rubber, acrylonitrile butadiene rubber (NBR), and epichlorohydrin rubber is used for the transfer belt.
In the conductive belt using the electroconductive rubber containing the conductive filler, it is difficult to disperse the conductive filler uniformly in the electroconductive rubber. Thus the electric resistance value varies according to a portion of the conductive belt. Therefore in the recent tendency, the ionic-conductive rubber is used more than the electroconductive rubber in the copying machine, the printer and the like required to have a high image quality by using digital image processing technique and color image processing technique.
To reduce a variation in the belt speed to cope with a high-speed operation of the printer and the like in recent years, the transfer belt is required to have a high elastic modulus. To allow the transfer belt to have a high elastic modulus, resins such as polyimide, PVDF, polycarbonate, and the like are used for the transfer belt.
A transfer belt of three-layer structure is disclosed in Japanese Patent Application Laid-Open No. 7-295391. More specifically, the dielectric layer made of urethane resin (surface resistance: 1012Ω) is formed on the inner layer made of chloroprene rubber or the like having an intermediate resistance. The dielectric layer is coated with a carbon-dispersed silicon solvent paint (surface resistance: 105–106) having a specific resistivity lower than that of the dielectric layer.
The conductive transfer belt disclosed in Japanese Patent Application Laid-Open No. 2000-10417 has the conductive elastic layer, the conductive intermediate layer having at least one conductive reinforcing layer containing any one of urethane resin, urea resin, and urethane-urea resin, and the conductive protection layer.
However, ionic-conductive rubber uniform in its electric resistance value does not have a high elastic modulus. On the other hand, it is difficult to allow the above-described resin having a high elastic modulus to be ionic-conductive. The electric resistance of the electroconductive rubber and the ionic-conductive rubber is adjusted by adding an electroconductive agent such as carbon black to the main component thereof. Thus both have a problem that the electric resistance varies in dependence on a portion thereof, i.e., is nonuniform in the electric resistance thereof.
The transfer belt of three-layer structure disclosed in Japanese Patent Application Laid-Open No. 7-295391 is intended to suppress separation discharge and provide the transfer belt which can deliver paper favorably, but not high in its elastic modulus and nonuniform in its electric resistance.
The following description is made in the specification of the conductive transfer belt disclosed in Japanese Patent Application Laid-Open No. 2000-10417: “The conductive substance to be contained in the conductive layer is not specifically limited, . . . the conductive carbon black and the ionic-conductive substance are added to the conductive reinforcing layer. (paragraph [0030])”. Apparently, the electroconductive agent consisting of the carbon black is added to the conductive reinforcing layer containing the ionic-conductive substance. Therefore the conductive transfer belt has room for improvement of the uniformity of its electric resistance.